The invention relates to vibrating hearth burners for use for example in solid fuel boilers and vapour generators. It is especially directed to such burners which can be used in boilers previously adapted for other fuels such as oil or gas.
The current energy crisis has prompted reconsideration of the use of solid fuel in various generation systems, particularly boilers and vapour generators. Primary factors in designing solid fuel systems are efficient combustion and ash removal, problems which do not arise where other fuels are used. The use of fluidized beds has greatly increased combustion efficiency, but on low capacity burners particularly it is difficult to achieve this with the simultaneous removal of fuel ash. Vibrating hearths, or travelling grates have been proposed in which the fuel moves along the grate as it burns such that the ash is discharged at the downstream end as fresh fuel is delivered at the upstream end, but while this provides a solution to the problem of ash removal it is not possible to ensure simultaneous efficient combustion and, perhaps more importantly, uniform combustion and pressure drop across the grate.
In one known vibrating hearth burner the grate is oscillated horizontally as fresh fuel is delivered to one end thereof. While appropriate selection of vibrating mechanism can accomplish forward motion of the fuel, it has to be carefully monitored to ensure that fresh fuel is properly ignited at the delivery end, and that burning fuel is not discharged with the ash. In such systems it can be necessary to cease the vibration on occasions to ensure proper combustion along the length of the grate. A consequence of this is increased dwell time of hot burning fuel on the grate and possible warping of the grate bars, introducing a further complication into the operation of the burner.